Calm Air – Aerospatiale ATR 42-300 – Spacing Issue

C-FCIJ, an Aerospatiale ATR 42-300 aircraft operated by Calm Air, was conducting IFR flight CAV569 from Churchill, MB (CYYQ) to Thompson, MB (CYTH). During the descent into CYTH, the flight crew cancelled IFR and positioned the aircraft to join the left downwind for Runway 06. CFUZY, a Swearingen SA226-TC aircraft operated by Perimeter Aviation, was conducting VFR flight PAG781 from CYTH to South Indian Lake (CZSN), MB. When CAV569 was approximately 15 nm North of CYTH, PAG781 was departing off Runway 06 under VFR. The flight crew of PAG781 advised CAV569 that they would be turning to the North West and climbing to 5500 feet ASL. CAV569 levelled at 5200 feet, and the CYTH FSS specialist requested that PAG781 level at 4500 feet. The flight crew of CAV569 subsequently climbed to 6000 feet in response to a TCAS RA to climb. The TCAS showed approximately 500 feet of vertical spacing as the two flights passed within ½ mile horizontally.